24/0 makes them grow faster, is the reason I usually use 24/0. That's not just something I read from a book; I did the experiment to be sure, with two exactly identical cabinets. The plants really do grow significantly faster and more vigorously under 24/0 (assuming you can keep the temps under control). You can shave about a week off veg time that way, roughly.

But no, don't change now. Changing the light schedule can cause hermies. If you start 18/6, stay 18/6. If you start 24/0, stay 24/0.